New rotors or not

[mdvineng]

I've got nail polish remover handy but Google says that may not be as good as pure acetone.

I've cleaned them again with petrol this morning. I'll wait till these pads come and see what result I get.

Acetone is available at chemists and even nail polish remover is better than petrol.

 

[kalex]

Acetone is available at chemists and even nail polish remover is better than petrol.

I thought petrol would be the optimum, it's just the fumes that make it not popular as it's hazardous

 

[2manyoranges]

ishaw speaks Deep Truth

Shimano brakes have a habit - a much hidden issue - of micro leaks on the piston seals. It sprays a lovely, fine spray of hydraulic oil onto the disk. Perfect for sh=t braking. You clean everything, think it's done, then two brake applications later....contamination all over the disc. It's random too. One set of Shimano (of the 10 or so we have) has lasted forever. Another started doing this ridiculous thing after 2 months. Irritating. It ruined a new pair of pads before I realised what was happening. Only answer is a new caliper, since unlike Hope and SRAM you can't do a caliper breackdown and seal repair. I am now converting one by one to Hope, since they are not far off the Shimano price right now. This might not be your problem but it sounds like it is....

 

[kalex]

Are you saying that if this is the problem I will have fine oil mist around the edge of the white pistons. I'm asking as I can have a look but the rear of the pads I took out were totally dry I think

 

[mattr]

Don't use petrol either! That's a pretty rubbish brake cleaner for bikes. Plenty of heavier oil fractions in there that will remain on your disc.
Something like IPA, Acetone, electrical contact cleaner (sort of brake cleaner, but no oil) or proper "bike" brake cleaner.

 

[mattr]

As far as I'm aware, it's not possible, under normal circumstances, to contaminate rotors to such an extent that they cannot be cleaned.

Some of the automotive cleaning/detailing stuff that people buy to make bikes shiny are all but impossible to remove, short of actually burning them off. I have a test car at work that had a handprint on the drivers side window that we had to actually mechanically scrape off. Nothing else touched it.
The window is now scratched, but doesn't have a goddamn handprint in the middle of it.

 

[mattr]

Are you saying that if this is the problem I will have fine oil mist around the edge of the white pistons. I'm asking as I can have a look but the rear of the pads I took out were totally dry I think

Yeah, they do look "totally dry" but they aren't.
Best way to test is to completely clean and dry the brakes, put a brake block in, wrap some tissue/toilet paper round the caliper and pull the lever to the bar, leave for a while, and you'll find oily toilet paper...

 

[kalex]

In answer to a few of above

I've got electrical cleaning stuff in my garage so may also give that a whirl.

I'll also try the method for testing for leaks.

I don't use and cleaning detailing stuff as I find it a pain just doing a quick soapy wash

 

[2manyoranges]

Mine were high end XT and failed unduly quickly. They too had the ceramic pistons....grrr….expensive. Toilet paper test a good one.

For cleaning nothing really beats isopropyl alcohol or MucOff brake cleaner (which is high grade acetone) - both also are excellent for starting mowers after the winter...plug out, squirt squirt, plug back in pull... bop bop cough bop bop bop.....off you go

 

[kalex]

Br-m8000 I think it said on the rear of the caliper.

I've googled caliper leak and it's definitely a large problem.

I'm going out to the garage to do the brake bleed and toilet paper trick to see if I have got any leaks before I get the new pads